The long-term objective of the proposed research is to understand the mechanisms that enable Epstein-Barr virus (EBV) to persist as a latent infection. The ability of EBV to persist within an immunocompetent host underlies the most significant pathology associated with this gamma-herpesvirus, namely the development of several distinct malignancies and lymphoproliferacive disease. Unfortunately, relatively little is known at the molecular level about the mechanisms that promote EBV persistence. Thus, the insight gained from these studies should contribute significantly to our understanding of EBV pathogenic potential and our ability to treat or prevent EBV-associated disease. To reach our objective, we will address two basic processes that contribute to EBV persistence and for which there are significant gaps in our knowledge. These are the regulation of EBV gene expression during restricted latency. i.e., the long-term virus carrier state, and the disruption by EBV of the host's innate immunity to virus infection. Three specific aims are proposed. Under Aim 1 we will address the mechanisms that regulate expression during restricted latency of the EBV protein EBNA-1, which is essential for maintenance of the EBV genome in tumor cells and for long-term viral persistence in normal latently infected B cells. Under Aims 2 and 3, we will address the mechanisms by which EBV inhibits the endogenous type I interferon (IFN) response and establishment of an antiviral state within latently infected B cells. Specifically, in Aim 2 we will focus on identification of the EBV protein(s) responsible for inhibition of the induction of type I IFN expression in response to EBV infection during the growth program of latency, which is crucial for establishment of the B-cell pool that serves as the long-term reservoir of EBV. Under Aim 3, we will address mechanisms by which EBV disrupts the host's innate antiviral response, focusing on the effects of EBV infection and individual EBV genes on known regulators of this response. Specifically, we will examine the biological significance of an observed physical interaction between the EBV LMP-1 protein and IRF-7, which mediates type 1 IFN-gene expression in response to viral infection. Additionally, we will address the significance of the suppression of several IFN-stimulated genes by the EBV EBER RNAs. In summary, the proposed research will evaluate fundamental mechanisms that promote EBV persistence and contribute to its success as a human pathogen, and thus should significantly broaden our understanding of EBV biology and our potential to target EBV-associated disease.